Plate heat exchanger for evaporation or distillation of liquids



Se t. 22, 1964 F. J. WENNERBERG 3,150,028

PLATE HEAT EXCHANGER FOR EVAPORATION OR DISTILLATION 0F LIQUIDS Filed July 11, 1961 2 Sheets-Sheet 1 CONDENSATE VAPOR CONDENSATE CONDENSATE CONCENTRATE 6a 7a 2 5a Fig. 2

INVHVTOR. Hv'lz Johan Wanner/berg PLATE HEAT EXCHANGER FOR EVAPORATION OR DISTILLATION OF LIQUIDS Filed July 11, 1961 2 Sheets-Sheet 2 FIG.3

bu INVENTOR. FRITZ la/MN WFA/NERBERG United States Patent 3,159,628 PLATE HEAT EXiIHANGER FGR EVAPORATEON 0R DHSTILLATEQN HF LTQUEDS Fritz Johan Wennerherg, Laud, Sweden, assignor to Aktieholaget Separator, Stockholm, Sweden, a corporation of Sweden Filed July 11, 1961, Ser. No. 123,191 Claims priority, application Sweden July 18, 19% 6 Claims. (Cl. 159-28) This invention relates to heat exchangers of the plate type and more particularly to an improved plate heat exchanger especially suitable for evaporation or distillation of liquids.

It has been previously known in the art to use plate heat exchangers for evaporating a liquid, such as milk, where the liquid is heated in every second space between the plates and thus gives off a part of its water content, while the remaining alternate spaces between the plates are filled with steam at a higher pressure and at a higher temperature than the milk, whereby the steam condenses and gives off the heat required for evaporation of the milk in the first-mentioned spaces between the plates. The evaporator is usually provided with several packs or groups of such plates operating at different temperatures and pressures, so that the steam escaping from the milk from one of the groups is used to heat the milk in the next plate group in order to reduce the steam consumption and thus ensure a more economical utilization of the steam. A multi-stage evaporator is thus obtained, wherein the milk proceeds through the different plate groups of the apparatus under falling pressure and temperature.

The mixture of milk and steam leaving the heated spaces between the plates in such a prior evaporator must be conveyed to special steam separation containers, located beside the plate heat exchanger, where the milk can separate from the steam. In order to convey the voluminous mixture from the various plate groups to the steam separation containers, it has been necessary to provide wide connecting plates inserted between the various groups in the plate heat exchanger and to which the large-sized pipe lines to the containers can be connected. Especially due to these containers, such an evaporator has required a very large floor area. Moreover, these free-standing containers with appurtenant pipe lines have occasioned considerable heat losses which have impaired the heat economy of the apparatus. The numerous pipe lines have also considerably increased the cost of the apparatus.

The principal object of the present invention is to provide a plate heat exchanger of the character described which overcomes the above-noted disadvantages.

According to the invention, the steam separation containers are given the shape of a box and replace the usual connection plates inserted between the plate groups in the plate heat exchanger. Each container is therefore provided at one side with a plate group where the milk is partly vaporized and at the other side with a plate group where the separated steam from the container condenses again. The steam separation containers are thus squeezed between the hot plate groups so that the heat losses are considerably reduced. This also has the advantage that the connection plates are eliminated and replaced by the above-mentioned containers. As the large-sized pipe lines are entirely eliminated, this evaporator requires hardly more space than previously required by the plate heat exchanger alone.

A threestage evaporator will thus consist of four plate groups or packs with three more or less box-shaped steam separation containers arranged between them. In

3,153,928 Patented Sept. 22, 1964 every second space between plates in the first plate group, a fraction of the milk is evaporated due to heating from the remaining plate interspaces filled with supplied steam which condenses in them. The steam evaporating from the milk in this first plate group passes directly (without flowing through external pipe lines) into the adjacent first container where the steam is separated from the milk. This milk may be recirculated to the first plate group by way of a special connecting channel, while the steam passes from this first container directly (without flowing through external pipe lines) to the next plate group where it is condensed in every second space between plates so as to give off heat to milk in the remaining spaces be tween plates. The latter milk, in turn, is partly vaporized and conveyed to the next container where a new separation of the steam from the milk occurs, and so on through the whole apparatus. In the last plate group, the steam is cooled and condensed by cold milk which has not yet been evaporated or by cooling water, or by both, whereupon the condensate is exhausted by a pump.

The new apparatus may be used for other purposes than evaporating milk, such as for producing fresh water from salt water. In its simplest form, the apparatus is constituted by two plate groups with a steam separation container arranged between them.

For a better understanding of the invention, reference may be had to the following detailed description in conjunction With the accompanying drawings, in which FIG. 1 is a schematic side elevational view, partly in section, of a three-stage evaporator embodying the invention, for evaporating milk,

FIG. 2 is a schematic illustration of the flow paths of the milk, the vapor and the cooling fluid in a plate heat exchanger according to FIG. 1, and

FIG. 3 is an exploded schematic view of the apparatus illustrated in FIG. 1, with some of the heat exchange plates omitted, showing the several flow paths through the apparatus.

Referring to FIG. 1, the evaporator comprises a frame 1, a supporting pillar 10, and upper and lower supporting rods 11 and 12 which are firmly secured to the frame 1 and extend horizontally therefrom to the pillar 1t). Rods 11-12 carry four plate groups or packs 2, 4-, 6 and 8 as well as the steam separation containers 3, 5 and 7 fitted between these plate groups. By means of end plate 9 and nuts 13 and 14 on the respective rods 11-12, it is possible to press the plate groups together so that the usual edge packings (not shown) on the plates can provide a tight joint between the plates and define their heat exchanging surfaces. The plate groups and the steam separation containers are shown in sectional view through the channels and the passages formed between plates and through which flows the milk, the mixture of milk and steam or the steam separated from the milk. The containers 3, 5 and 7 can each be provided with a splash guard or wire gauze insert 15, or the like, in order to facilitate the separation of the steam from the milk.

The preheated milk to be evaporated is admitted via the pipe 16 to the through-flow channel 18 in the first plate group 2 and flows upward to channel 17 by way of every second space between plates in the group 2, the milk being heated during this upward flow in parallel streams. The resulting mixture of milk and steam is then delivered from channel 17 through opening 17a (FIG. 3) in the adjacent end wall of the container 3 where the milk is separated from the steam and collected in the lower part of the container 3, from which it flows again into the plate group 2 via the channel 18 and the end wall opening 18a leading thereto (FIG. 3). Consequently, the milk circulates through the plate group 2 where evaporation occurs and through the subsequent container 3 where steam separation occurs. The separated vapor is admitted from container 3 into the top of the adjacent plate group 4 via a suitable opening 26b (FIG. 3) in the adjacent wall of container 3 and is condensed in this unit by flowing through alternate plate interspaces lying between those through which the milk flows. The steam condensate formed in plate group 4 is discharged from the plate heat exchanger by a drain pipe 27a (FIG. 3) at the bottom. Milk from lower outlet Zita of container 3 is admitted to the lower channel 29 of the group 4 and is evaporated in the latter unit in the same way as in the group 2. The milk circulates in the plate group 4 and in the container 5 in the same way as in group 2 and container 3. Con sequently, the milk flows through the plate groups and the containers to the last container 7 under continuous evaporation. The concentrated milk is discharged from container 7 through a lower outlet 21. The ultimate outgoing steam from container 7 condenses in the last plate group 8 and the condensate via heat loss to the cold milk feed is discharged through the lower outlet 22.

As shown in FIG. 2, the milk inlet 16 leads through the frame 1 and communicates through the plate groups or packs and the containers 2-6 of the apparatus with the last container 7, from which the concentrated milk is discharged through the outlet pipe line 21. Pipe lines 23 and 24 supply steam to and discharge condensate from the heating plate interspaces of the plate group 2. Pipe lines 25 and 26 lead milk or cooling fluid to and from the interspaces 8a of the last plate group forming cooling section 8. The condensate of the steam obtained from the milk is discharged from plate groups 4', 6 and 8 through pipe lines 27, 28 and 22 extending partly through the containers 5 and 7 (as shown at 27a and 28a in FIG. 3) and the end plate 9, respectively to common discharge line 30. Reducing valves 29 in line 30 make it possible to obtain a dropping steam pressure in the various sections of the plate heat exchanger when the milk, the steam and the condensate flow through the apparatus. Instead of a special frame I, one of the steam separation containers 3, 5 or 7 can be designed as a frame. This container is then preferably provided with a pedestal which may be placed on the floor so that this container can support plate groups, steam separation containers and two end plates, for the frame must in this case be replaced by an end plate such as that indicated at 9 in FIG. 1.

In FIGS. 2 and 3, the reference numerals 2a, 4a and 6a indicate generally the channels and plate interspaces for the milk flow through the respective plate groups 2, 4 and 6, While reference numerals 2b, db and 6b indicate generally the channels and alternate plate interspaces for the steam and condensate flow through the respective plate groups. The milk flow through containers 3, 5 and 7 is indicated at 3a, 5a and 70, respectively, and the steam flow through these containers is indicated at 3b, Sb and 712, respectively. Steam outlet 20b leads from the upper portion of container 3 through the adjacent end of pack 4 into its part 41), there being similar steam outlets from containers 5 and 7 to the plate interspaces 6b and 8!), respectively.

A two-stage evaporator will consist of three plate groups and two intermediate containers incorporated in the plate groups, and a one-stage evaporator will consist of two plate groups with an intermediate container.

Such a plate heat exchanger can also be used for other purposes than to concentrate a liquid. For example, it can be used to clear a liquid from solid substances or from substances dissolved in the liquid. Thus, it can be used for producing pure and salt-free drinking water or feed water for steam boilers from polluted or salt water. In this case, the pure salt-free condensate (the liquid obtained at the common outlet pipe 30 from pipes 27, 28 and 22) is collected, while the polluted or salt water discharged at the outlet 21 is drained off.

The plate groups 2, 4, 6 and 8, each comprising essentially a pack of spaced heat exchange plates, are Well known and are therefore shown only schematically. Each plate is generally provided with two upper and two lower through-flow holes, an upper one of which supplies a heating fluid and a lower one discharging it (usually as a condensate), while another lower hole supplies the product to be evaporated and another upper hole discharges this product. The plates are spaced from each other by packing members or gaskets which also serve in conjunction with the holes to define the flow paths for the respective fluids through the plate groups by way of the plate interspaces, as will be readily understood by those skilled in the plate heat exchanger art.

It milk is to be evaporated, it is first preheated by being supplied at 25 in FIGS. 2 and 3 and discharged at 26, whereupon the milk is supplied directly to the pipe line 16, as indicated at 2611. In FIG. 1, the recirculation of liquid through the plate group 2 and the container 3 as well as between the plate group and the container 5, etc., can in certain cases be dispensed with, in which case the direct connections between container 3 and channel 18 and between container 5 and channel 2%, respectively, can be closed in any suitable manner, as by flanges (not shown). As long as these connections are open, not only is the above-mentioned recirculation obtained but also an equalization is obtained of the liquid level in the respective containers, which constitutes a guarantee against boiling dry. Moreover, the liquid level in each container can be controlled by the reducing valves 2% located in the milk concentrate outlet openings Zita of containers 3 and 5.

I claim:

1. In a plate heat exchanger for evaporation or distillation of a liquid forming a heat-absorbing medium, the combination of first and second aligned packs of heat exchange plates arranged vertically, the plates of each pack forming intercommunicating plate interspaces for throughflow of a hea -absorbing medium alternating with and separated from intercommunicating plate interspaces for throughfiow of a heat-emitting medium, said interspaces for the heat-emitting medium in the first pack havmg an inlet and an outlet for said heat-emitting medium, a vapor separation container clamped between the aligned plate packs and having opposite end plate walls serving also as the adjacent end plates of the respective adjacent packs, one of said end walls having an opening leading directly to the upper portion of the container from the upper portion of said interspaces for the heat-absorbing medium in said first pack, said interspaces for said liquid heat-absorbing medium in said first pack having an inlet for said heat-absorbing medium, whereby the container is adapted to receive directly from said interspaces for the liquid heat-absorbing medium in the first pack a mixture of said liquid and its vapor formed from the liquid by the heating action of said heat-emitting medium in the other interspaces in said first pack, the container having in its opposite end wall an opening forming a vapor outlet leading directly from the upper portion of the container to the upper portion of said interspaces for the heat-emitting medium in said second pack, the container also having in said opposite end wall a second open ing directly connecting the lower portion of the container to the lower portion of said interspaces for the heat-absorbing medium in said second pack, said second pack having separate outlets from said interspaces for the heat-emitting medium as condensate and for the heatabsorbing medium as concentrate, respectively.

2. The combination defined in claim 1, in which said one end wall of the container also has an opening direct ly connecting the lower portion of said container to the lower portion of said interspaces for the heat-absorbing medium in said first pack.

3. The combination defined in claim 1, comprising also a pressure-reducing valve in a discharge line from said separate outlet from said interspaces for the heatemitting medium in the second pack.

4. The combination defined in claim 1, comprising also a pressure-reducing valve in said second opening of the container.

5. In a plate heat exchanger for evaporation or distillation of a liquid forming a heat-absorbing medium, the combination of at least three aligned packs of heat exchange plates arranged vertically, the plates of each pack forming intercomrnunieating plate interspaces for throughflow of a heat-absorbing medium alternating with and separated from intercommunicating plate interspaces for throughflow of a heat-emitting medium, a vapor separation container clamped between each pair of plate packs to form a row including first and last packs and first and last containers located, respectively, between said first and last packs and an intermediate pack, the interspaces for the liquid heat-absorbing medium in the first pack having an inlet for said liquid, each container having opposite end plate walls serving also as the adjacent end plates of the respective adjacent packs, one end wall of each container having an opening leading directly to the upper portion of the container from the upper portion of said interspaces for the heat-absorbing medium in the preceding pack, the opposite end wall of each container having an opening forming a vapor outlet leading directly from the upper portion of the container to the upper portion of said interspaces for the heat-emitting medium in the next succeeding pack, each container except said last container having in said opposite end wall a second opening leading directly from the lower portion of the container to the lower portion of said interspaces for the heatabsorbing medium in the next succeeding pack, said last container having a bottom outlet for the liquid heatabsorbing medium, and a vapor condensate discharge pipe leading from said interspaces for the heat-emitting medium in each of the intermediate and last packs, said interspaces for the heat-emitting medium in the first pack having an inlet and an outlet for said heat-emitting medium, whereby the first container is adapted to receive directly from said interspaces for the liquid heat-absorbing medium in the first pack a mixture of said liquid and its vapor formed from the liquid by the heating action of said heat-emitting medium in the other interspaces in said first pack.

6. The combination defined in claim 5, in which said one end wall of the first container has a second opening directly connecting the lower portion of the first container with the lower portion of said interspaces for the heatabsorbing liquid medium in said first pack.

References Cited in the file of this patent UNITED STATES PATENTS 1,216,187 Trump Feb. 13, 1917 1,318,793 Newhall Oct. 14, 1919 2,012,668 Jahn Aug. 27, 1935 2,073,738 Faber Mar. 16, 1937 2,314,966 Astle Mar. 30, 1943 2,392,021 Wildermuth Jan. 1, 1946 2,510,233 Kremer June 6, 1950 2,562,739 Risberg July 31, 1951 2,746,536 Sumiya May 22, 1956 2,796,120 Lockman June 18, 1957 2,896,705 Ramen July 28, 1959 2,960,160 Goodman Nov. 15, 1960 

1. IN A PLATE HEAT EXCHANGER FOR EVAPORATION OR DISTILLATION OF A LIQUID FORMING A HEAT-ABSORBING MEDIUM, THE COMBINATION OF FIRST AND SECOND ALIGNED PACKS OF HEAT EXCHANGE PLATE ARRANGED VERTICALLY, THE PLATES OF EACH PACK FORMING INTERCOMMUNICATING PLATE INTERSPACES FOR THROUGHFLOW OF A HEAT-ABSORBING MEDIUM ALTERNATING WITH AND SEPARATED FROM INTERCOMMUNICATING PLATE INTERSPACES FOR THROUGHFLOW OF A HEAT-EMITTING MEDIUM, SAID INTERSPACES FOR HEAT-EMITTING MEDIUM IN THE FIRST PACK HAVING AN INLET AND AN OUTLET FOR SAID HEAT-EMITTING MEDIUM, A VAPOR SEPARATION CONTAINER CLAMPED BETWEEN THE ALIGNED PLATE PACKS AND HAVING OPPOSITE END PLATE WALLS SERVING ALSO AS THE ADJACENT END PLATES OF THE RESPECTIVE ADJACENT PACKS ONE OF SAID END WALLS HAVING AN OPENING LEADING DIRECTLY TO THE UPPER PORTION OF THE CONTAINER FROM THE UPPER PORTION OF SAID INTERSPACES FOR THE HEAT-ABSORBING MEDIUM IN SAID FIRST PACK, SAID INTERSPACES FOR SAID LIQUID HEAT-ABSORBING MEDIUM IN SAID FIRST PACK HAVING AND INLET FOR SAID HEAT-ABSORBING MEDIUM, WHEREBY THE CONTAINER IS ADAPTED TO RECEIVE DIRECTLY FROM SAID INTERSPACES FOR THE LIQUID HEAT-ABSORBING MEDIUM IN THE FIRST PACK A MIXTURE OF SAID LIQUID AND ITS VAPOR FORMED FROM THE LIQUID BY THE HEATING ACTION OF SAID HEAT-EMITTING MEDIUM IN THE OTHER INTERSPACES IN SAID FIRST PACK, THE CONTAINER HAVING IN ITS OPPOSITE END WALL AN OPENING FORMING A VAPOR OUTLET LEADING DIRECTLY FROM THE UPPER PORTION OF THE CONTAINER TO THE UPPER PORTION OF SAID INTERSPACES FOR THE HEAT-EMITTING MEDIUM IN SAID SECON PACK, THE CONTAINER ALSO HAVING IN SAID OPPOSITE END WALL A SECOND OPENING DIRECTLY CONNECTING THE LOWER PORTION OF THE CONTAINER TO THE LOWER PORTION OF SAID INTERSPACES FOR THE HEAT-ABSORBING MEDIUM IN SAID SECOND PACK, SAID SECOND PACK HAVING SEPARATE OUTLETS FROM SAID INTERSPACES FOR THE HEAT-EMITTING MEDIUM AS CONDENSATE AND FOR THE HEATABSORBING MEDIUM AS CONCENTRATE, RESPECTIVELY. 